<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>

    *{
      margin: 0;
      padding: 0;
    }

    .container{
      width: 1000px;
      height: 800px;
      margin: 0 auto;
    }
    ul,li{
      list-style: none;
    }

    .list{
      margin-top: 40px;
      border-bottom: 1px solid #333;
    }
    .clearfix::after{
      content: " ";
      display: block;
      clear: both;
      height: 0;
      overflow: hidden;
    }

    /* 伪元素实现单侧边框 */
    .item{
      width: 100px;
      height: 50px;
      line-height: 50px;
      text-align: center;
      margin-left: 50px;
      font-size: 16px;
      color: #666;
      /* background: powderblue; */
      float: left;
      position: relative;
      /* cursor:all-scroll; */
      /* border-bottom: 1px solid #333; */
    }
     .second::before{
      content: " ";
      width: 100%;
      left: 0;
      bottom: 0;
      position: absolute;
      border-bottom: 3px solid rgb(209, 52, 52);
    }

    /* 伪元素实现三角形 */
    .triangle{
      width: 400px;
      height: 400px;
      margin-top: 50px;
      /* background: powderblue; */
      position: relative;
    }

    .triangle::before{
      content: " ";
      border-top: 200px solid transparent;
      border-bottom: 200px solid rgb(199, 62, 117);
      border-left: 200px solid transparent;
      border-right: 200px solid transparent;
      position: absolute; 
    }

  </style>
</head>
<body>
  <div class="container">
    <!-- 伪元素实现单侧边框 -->
    <ul class="list clearfix">
      <li class="item">精绝古城</li>
      <li class="item second">龙岭迷窟</li>
      <li class="item">云南虫谷</li>
      <li class="item">昆仑神宫</li>
      <li class="item">南海归墟</li>
      <li class="item">巫峡棺山</li>
    </ul>
    <!-- 伪元素实现三角形 -->
    <div class="triangle"></div>
  </div>
</body>
</html>